1. Field of the Invention
The present invention relates to a fixing member. In addition, the present invention also relates to a fixing device and an image forming apparatus using the fixing member.
2. Discussion of the Related Art
The mainstream of electrophotographic image forming apparatuses such as copiers and printers are switching from monochrome to full-color recently. A typical full-color electrophotographic image forming apparatus includes an image forming part that forms a full-color toner image comprising cyan, magenta, yellow and black toner images on a recording medium, and a fixing device that fixes the full-color toner image on the recording medium. The fixing device includes a heating device that heats a toner image on a recording medium, a fixing member that fixes the toner image on the recording medium, and a pressing member that forms a fixing nip between itself and the fixing member. When a recording medium having a toner image thereon passes through the fixing nip, heat and pressure are applied to the toner image, thereby fixing the toner image on the recording medium.
Belt-shaped and roller-shaped fixing members are widely used so far. For example, a substrate such as a metallic roller or a resin seamless belt on which an elastic layer made of a heat-resistant rubber, etc. is provided, and that on which a release layer is further provided on the elastic layer have been widely used as fixing members. A roller-shaped fixing member may be integrated with a heating device. The resulting heating fixing roller may include a heating device interiorly. A belt-shaped fixing member may also be integrated with a heating device. In this case, the heating device may be provided in the interior of the seamless belt stretched taut by rollers.
Fixing members are supposed to evenly heat a full-color toner image which generally comprises four color toner images. Therefore, fixing members are required to flexibly and intimately contact toner images to effectively transmit heat thereto. To respond to this requirement, silicone rubbers are widely used for fixing members because of having both flexibility and heat resistance. However, since silicone rubbers have low thermal conductivity, the speed of heat conduction to toner images may be low. When heat is conducted slowly, it may take a long time until the surface of a fixing member is heated to a temperature sufficient to fix toner images. In particular, with regard to high-speed image forming apparatuses, sufficient heat may not be supplied to toner images within an appropriate time. Additionally, warm-up time of image forming apparatuses may also be lengthened because warm-up speed of fixing members generally controls that of image forming apparatuses.
In attempting to solve the above-described problem, Japanese Patent Application Publication No. (hereinafter JP-A) 2005-292218 and JP-A 2006-133576 disclose fixing members having an elastic layer including a silicone rubber. The silicone rubber contains a filler having high thermal conductivity, such as aluminum nitride and a high-density carbon fiber, to improve thermal conductivity of the elastic layer. This approach advantageously increases the heat supply speed on the one hand, but disadvantageously increases the specific density of the fixing member on the other. As a result, heat capacity of the fixing member may be so large that warm-up time may not be shortened.
JP-A 2008-191557 and JP-A 2008-197585 disclose fixing members having an elastic layer including a silicone rubber, carbon fibers and voids, and a release layer including a fluorine-based resin on the outermost surface. Advantageously, fluorine-based resins have excellent releasability from toner owing to their low surface energy and nonadhesive property. At the same time, fluorine-based resins have high hardness. Therefore, when heat and pressure are applied to toner particles at a fixing nip to fix them on a recording medium, the toner particles may be excessively compressed, which results in deterioration of the resultant image resolution. Additionally, such an elastic layer with high hardness may not precisely follow roughness of the surface of a recording medium, which results in unevenness of the resultant image.
JP-A 2006-18173 further discloses a fixing member having a rubber-made elastic layer having both flexibility and toner releasability. However, this fixing member still has not solved the problem of thermal conduction.